Known contact type torque sensors are used e.g., for vehicle steering devices (as disclosed in the below-identified Patent document 1). A non-contact type torque sensor is known which include two magnetic angle sensors arranged coaxial with a shaft and capable of detecting absolute rotation angles. These angle sensors convert the absolute rotation angles, which correspond to the rotational displacement at the respective axial positions, to output signals. When the shaft is twisted under torque applied to the shaft, the shaft is rotationally displaced about its axis to different degrees at two axially separate points. Thus, by detecting the rotational displacements at the two axially separate points as absolute rotation angles, the twist angle between these two axially separate points is given as the difference in output between such absolute rotation angles. Since there is a correlation based on the structural specifications of the shaft between the torque applied to the shaft and the twist angle of the shaft, it is possible to indirectly measure the torque applied to the shaft based on the difference in output between the absolute rotation angles and the above known correlation. This type of torque sensor units are therefore detectors configured to convert the torque applied to the shaft to absolute rotation angles at the above-mentioned two axially separate points.
There is known a magnetic angle sensor including at least one magnetic sensor element and at least one magnet which is arranged concentric with a shaft member so as to be rotationally displaced corresponding to the twist angle of the shaft member. As the magnet is rotationally displaced, the magnetic field generated by the magnet rotates relative to the magnetic sensor element, and the magnetic sensor element converts the change in magnetic flux density due to the rotation of the magnetic field to an electrical signal. Based on the electrical signal, the magnetic angle sensor generates an output signal corresponding to the absolute rotation angle.
Such magnetic angle sensors include a Vernier type sensor, which include a primary scale magnet including a plurality of pairs circumferentially arranged magnetic poles, and a Vernier magnet arranged so as to be concentric with the primary scale magnet and including a plurality of pairs of magnetic poles, wherein the total number of pairs of magnetic poles of the primary scale magnet is different than the total number of pairs of magnetic poles of the Vernier magnet, a first magnetic sensor element for detecting the density of the magnetic flux generated by the primary scale magnet, and a second magnetic sensor element for detecting the density of the magnetic flux generated by the Vernier magnet (see the below-identified Patent document 2 and Non-patent document 1).
There is also known a torque sensor unit including first and second magnetic angle sensors each including a cylindrical magnet magnetized in its diametrical direction, a first magnetic sensor element for detecting the tangential component of the magnetic field generated by the cylindrical magnet, and a second magnetic sensor element for detecting the radial component of the magnetic field (see the below-identified Patent document 3).